The present invention relates to a vacuum pump, and more particularly to an improvement of a diaphragm vacuum pump to be driven by an engine of a vehicle to supply vacuum to pneumatically operated devices with which the vehicle is equipped.
Conventional vacuum pumps of this type are generally so constructed as to effect reciprocation of a diaphragm piston by swinging operation of a rocker arm engaged with an eccentric cam driven by the vehicle engine. With the conventional vacuum pump, a disadvantage has been experienced because of damage to the valve devices of the pump by the piston when the upper dead point of the piston is raised up by wear or defacement of the engaging faces of the cam and the rocker arm in course of the operation of the pump. Furthermore, the obtainable vacuum degree is much influenced by the volume difference within a pressure reduction chamber, the volume difference being decided by the positions of the upper and lower dead points of the diaphragm piston.